For the purpose of equipping strands of electric cables that are ready to connect it is known to place end sleeves on the skinned strand encompassing the wires of the strand and then to press the end sleeve in such a manner that said sleeve is given a rigid, immobile seat. The connection of the strand is then made through a screw connection at the connecting position, said screw connection pressing on the pressed end sleeve. The end sleeves have a circular cross section in the unpressed condition. In accordance with DIN standards it is provided that after the pressing the sleeve should have a trapezoidal cross section in order to achieve a particularly tight connection between the end sleeve and the strand.
A crimp tool of the type mentioned above, which can be universally used for cross-sectional areas between 0.5 and 4.0 mm, is arranged in accordance with the principle of scissors, i.e. each of the jaws forms one part with the handle and the two parts are connected to each other by means of an axle journal. The two cheek plates are flexibly suspended in the jaws and guided against each other and form a pressing position whose axis lies in the main extension plane of the crimp tool, whereby the pressing can be made with said tool either at the front end or head end. The resilience for overcoming the differences in the path is achieved in this tool in such a way that the jaws each comprise in the centre a recess with an open edge extending from the flexible pivot bearing in the direction towards the handles, whereby the axle journal is arranged in the area of said jaws. The jaws thus form spring jaws or yielding springs. The frontal arrangement of the pressing position is preferable here. There is the disadvantage, however, that because of the arrangement of the handles and the jaws in one single piece only a simple lever transmission of the drive is possible, so that the crimp tool requires relatively high pressing forces. In addition, the described resilient or flexible arrangement of the jaws and their load may lead to material fatigue. The spring forces supplied by the jaws are, in addition, highly dependent on the adherence to narrow tolerances of the cross sections of the jaws. A change in the material thickness or even a deviation in the predefined hardness will change the elasticity properties of the tool, so that no reproduceable results can be expected for the respective tolerances. If an end sleeve with a larger cross section than the maximally provided cross section is inserted and pressed, there is the danger that the resiliently arranged jaws are subjected to plastic deformation, so that the crimp tool can no longer be used in the proper manner.
A further crimp tool arranged as a universal crimp tool comprises two cheek plates with only a single pressing position, i.e. a single mould for deforming strands of varying thickness. The universal pliers can press strands with a cross section between 0.5 to 4.0 mm. When pressing strands with a small cross section, for example 0.5 mm, the cheek plates close fully or nearly fully at the time at which the drive has covered its maximal path, e.g. when the handles are pressed together at a maximum. When pressing larger cross sections, for example 4.0 mm, the pressing position remains relatively open, i.e. the cheek plates must end their path earlier by including the material of the strand, whereas otherwise the drive always covers an identical path in all cases. In order to compensate the differences in the path this tool also comprises a flexible pivot bearing on the jaws of the crimp tool. The one jaw is rigidly connected to the handle, i.e. they are made of one single piece. A bent lever acts upon the other jaw as drive, said drive being actuated by means of the other handle. The two jaws are swivellably held about an axle journal in the manner of a rocking lever. The jaw driven by the bent lever drive is exclusively swivellably held on the axle journal by means of a cylindrical bore, whereas the other jaw embraces the axle journal with an oblong hole which is arranged in the jaw parallel to the direction of movement of the cheek plates during the pressing. In the jaw forming a part with the handle a horseshoe-like yielding spring is swivellably suspended in a hinge pin, whose other end acts upon the axle journal of the two jaws. When pressing cross sections of varying thickness the yielding spring allows the one jaw to yield relative to the other jaw and thus the one cheek plate relative to the other plate, although the identical path is covered with the drive in the jaws. The cross-sectional ranges that can be pressed are limited to cross sections between 0.5 and 4.0 mm. Preferable in this crimp tool is the arrangement of the cheek plates, which allow the insertion of the end of the strand and the end sleeve transversally to the main extension plane of the crimp tool, so that the conicalness of the pressed end sleeves is prevented. The relative arrangement of the pressing position is disavantageous with respect to the fact that, for example, difficulties could arise in cramped switch cabinets. The horseshoe-like yielding spring, which is provided in double arrangement and in allocation to the one jaw, is subjected to considerable wear and tear by pressing larger cross sections, that there is the danger of material fatigue. The cheek plates are arranged on the jaws, but are not swivellable with respect to said jaws, so that the cheek plates assume the scissors -movement of the jaws even during the closing process. This scissors movement leads to the formation of flaps on one side during the pressing, i.e. the pressed cross section does not have a symmetrical form.
A further known universal crimp tool comprises a jaw driven through a bent lever drive. The one jaw is parted towards the handle, whereby a plastic block is arranged in a cuboid casing, said block being compressible through an end plate arranged on the handle, so that the required path differences on the cheek plates are achieved in such a way. The two cheek plates are swivellably held on a common axle journal without the arrangement of an oblong hole. The swivellability of the parted jaw is limited between stops, so that there are limits in the compression of the plastic block. The cheek plates are flexibly suspended on the jaws and guided against each other, whereby they engage with each other in a comb-like manner and form a pressing position having an approximately square outline, whereby the axis of said pressing position lies in the main extension plane or direction of the tool. This arrangement is beneficial for the use of the crimp tool in cramped conditions, e.g. in a switch cabinet. It is furthermore preferable that this tool can process a larger cross-sectional area between 0.5 to 6.0 mm. The disadvantage consists of the fact, however, that the pressing cross section is not equivalent to the desired trapezoidal cross section, but approximately square. By the respective arrangement of the cheek plates the pressing is carried out in each plane transversal to the axis of the strand only on two opposite positions or surface areas, whereas the two other surface areas which are displaced by approx. 90.degree. sag freely and can thus deform against the pressing power acting upon them. The form produced by the pressing is thus not optimal and does not fulfill DIN standards. Furthermore, the disadvantage arises that the pressed end sleeves have a slightly conical form, in particular in the event that comparably short end sleeves are used which cannot be inserted into the pressing position symmetrically to the hinge points of the cheek plates. This conicalness tapers precisely in the direction in which the end sleeve can be pulled out from its connecting position, so that there is the danger that in the event of the loosening of the screw connection or the movement of the strand the screw connection comes undone.
From the DE-AS 21 49 167 a crimp tool is known with which it is possible to optionally press different cross sections. However, a special pressing position is provided in the cheek plate for each cross section, so that the tool does not concern a universal crimp tool. In this known crimp tool there is the danger that the pressing positions are confused, so that the pressing takes place at the wrong pressing position. In addition, it needs additional handling next to the necessary special attention.